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Therapeutic Monitoring of Clozapine in Australia: The Need for Consensus

Oo, Thein Z MBChB*; Wilson, John F PhD; Naidoo, Divania BSc (HONS)*; Chetty, Manoranjenni PhD*

doi: 10.1097/01.ftd.0000245381.72316.0b
Short Communication

In the absence of well-defined guidelines for the monitoring of plasma concentrations of clozapine, this study examined the practices of seven laboratories from four states in Australia. Laboratories analyzed 5 freeze-dried serum samples containing a mixture of clozapine and norclozapine in varying concentrations and the measurement data were analyzed for accuracy and precision. Additional information on laboratory practices was obtained through questionnaire responses. Measurement precision amongst the laboratories was good but there were significant differences in the accuracy of measurements from one laboratory. There were differences in the ranges for which assays had been validated and in suggested therapeutic ranges. These differences could have a significant impact on the interpretation of measured concentrations and patient care, and emphasize the need for consensus in this area. Repeat concentration measurements are recommended in the case of drug concentration measurements that are inconsistent with clinical observations or previous measurements.

From the *Faculty of Pharmacy, University of Sydney, NSW 2006, Australia; and †Department of Pharmacology, Therapeutics and Toxicology, Wales College of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom.

Supported in part by a University of Sydney Sesqui Grant.

Reprints: Manoranjenni Chetty, PhD, Building A15, Faculty of Pharmacy, University of Sydney, NSW 2006, Australia (e-mail:

© 2006 Lippincott Williams & Wilkins, Inc.